1. Field of the Invention
The present invention relates to a process for producing organo phosphazene polymers, for which many industrial applications have now been developed in various fields. Organophosphazene polymers have excellent properties such as heat-resistance, flame-resistance, and oil-resistance and can be useful as flame retardants, lubricant oils, electric insulators or hydraulic oils. Recently, medical applications have been also studied actively, such as sutures, artificial blood vessels and artificial internal organs owing to the innocuous properties of the organophosphaznen polymers and their metabolites to living body.
2. Description of the Prior Art
Cyclic chlorophosphazene trimer, especially, cyclic dichlorophosphazene trimer (hereinafter referred to as "3PNC") polymerizes to linear polymers at elevated temperatures. For the production of organophosphazene polymers, the chlorophosphazene polymers are reacted with organic hydroxy compounds to substitute the chlorine atoms bonded to the phosphorus atoms in the phosphazene skeleton (hereinafter referred to as "active chlorine atoms") with the hydroxy compounds. Various methods for producing organophosphazene polymers are illustrated in "Phosphorus Nitrogen Compounds", pp. 354-356, written by H. R. Allcock, Polymeric Materials: Science and Engineering, vol. 53, pp. 118-122, written by Austin and H. R. Allcock. These methods may be generally classified into the following three groups:
(1) the reaction of alkali metal salt of hydroxy compounds,
(2) the reaction of hydroxy compounds using a tertiary amine as an acid acceptor,
(3) the reaction of alkali metal salt of hydroxy compounds using a quaternary ammonium salt as an acid acceptor.
However, the method (1) described above takes an extremely long reaction time to completely replace all the active chlorine atoms. In the method (2) described above, it is generally difficult to replace all the active chlorine atoms entirely. The method (3) described above requires an expensive catalyst in a considerably great amount and a relatively long reaction time for the completion the reaction.
Further, since all the known reactions described above are conducted under heating, when introducing such substituents as unsaturated aliphatic groups which polymerize easily, it is inevitable to form by-products by polymerization.
On the other hand, the present inventors found a similar method to the present invention and filed a U.S. patent application Ser. No. 157,321 on Feb. 18, 1988. In the method, aryloxyphosphazene oligomers are produced by the substitution of chlorine atoms of chlorophosphazene oligomers such as 3PNC with aryloxy groups.